Field of the Invention
The present invention relates to a nano vacuum gap power switching semiconductor device, and in particular to a device which has improved frequency range, reduced noise and increased power handling capability facilitated by the gate all-around cathode design and a nano scale vacuum gap design.
Discussion of the Prior Art
Vacuum gap power handling devices are known. Such devices consist of a cathode, an anode spaced apart from the cathode, and a control electrode (often called Gate) adjacent the cathode and the anode. In general, the cathode is a pointed structure from which electrons are emitted when subjected to an electric field of sufficient strength. The anode provides the necessary electric field, and the control electrode controls the flow of electrons from the cathode to the anode.
One skilled in the art understands that some vacuum gap devices may operate at room temperature, and that cathodes in such devices are termed ‘cold-cathodes’. The operating temperature of vacuum gap devices in the present invention is not germane to the present invention. In the present application, the term ‘cathode’ is intended to include devices operating at both room temperature and other operating temperatures. The terms ‘cold-cathode’ and ‘cathode’ are used interchangeably in the present application.
One example is a vacuum power switch using carbon nanotubes as the electron cathode. Such a vacuum power switch comprises a cathode, an anode and a current switching grid between the cathode and the anode, in which the cathode comprises an array of aligned carbon nanotubes extending toward the anode. The anode is a plate fabricated opposed to the carbon nanotube cold-cathode. The control electrode is fabricated as a grid located between the cold-cathode and the anode. In this example, the grid or gate to cathode separation is relatively large requiring a large gate bias to effectuate the necessary electric fields.
Another example of a power switching device of field-emission type is one using a tip array. Such a device comprises an emitter electrode, an anode electrode, a cone-shaped emitter, and a gate [control] electrode. When a high voltage is applied between the emitter electrode and the anode electrode, the emitter emits electrons, whereby main current flows. The main current is controlled by supplying a control signal to the gate. This example requires a large bias due to relatively large grid and cathode separation.
A third example is a micro power switch that uses a cathode with a tip structure, and a driving method to control the flow of electrons. A micro power switch according to this third example comprises: a cold cathode for emitting electrons; an anode for capturing the electrons emitted from the cold cathode; and a control electrode for controlling an amount of the electrons emitted from the cold cathode. The cold cathode is made of material having a smaller electron emission barrier as that of the control electrode. The anode is applied with a positive potential in relation to the cold cathode, and the control electrode is applied with a potential equal to or lower than a potential of the cold cathode. In this condition, the electron emission from the cold cathode is stopped. This example also requires relatively large bias voltage due to the relatively large cold-cathode to control electrode distance.
There is a compelling need in this industry for a semiconductor based vacuum gap power switch that provides for a highly efficient electron emission without a need for a large gate bias that allows for high frequency, high power and low noise operation. This invention fills this critical need.